This invention relates to a fuel injection valve for internal combustion engines, which can be controlled in injection rate and injecting direction in response to operating conditions of the engine.
Fuel injection valves generally employed in Diesel engines are typically comprised of a nozzle body having an end wall formed with at least one nozzle hole, and a nozzle needle slidably received in an axial hole formed in the nozzle body for closing and opening the nozzle hole. Pressurized fuel from a fuel injection pump forcibly lifts the nozzle needle to open the nozzle hole to thereby cause injection of the fuel.
According to such conventional fuel injection valves, due to the pressure characteristic of fuel supplied thereto that the fuel pressure varies in proportion to the rotational speed of the engine, if the discharge area of the nozzle hole or the lifting stroke of the nozzle needle is set at a value appropriate to operation of the engine under a high speed/high load condition, the set value turns out too large for operation of the engine under a low speed/low load condition, which results in too low an injection pressure, often causing abnormal injection.
To overcome this disadvantage, several improved fuel injection valves have been proposed, for instance, a fuel injection valve of variable valve opening pressure type disclosed by Japanese Provisional Patent Publication No. 57-102527, which employs two nozzle springs urging the nozzle needle in the valve closing direction and operable such that when low fuel pressure acts upon the nozzle needle, one of the nozzle springs is compressed, while when high fuel pressure acts upon the nozzle needle, both of the nozzle springs are compressed, to thereby vary the lifting stroke of the nozzle needle in two steps, and a fuel injection valve of nozzle needle lift-controlled type disclosed by Japanese Provisional Patent Publication No. 56-141051, which employs a plunger controlled to restrain lifting of the nozzle needle by means of a control valve formed e.g. of a spool valve operable in response to operating conditions of the engine, to thereby vary the lifting stroke of the nozzle needle in two steps.
These proposed fuel injection valves resort to a common measure to overcome the aforementioned disadvantage, that is, when the engine is operating under a low speed/low load condition including an idling condition, the lifting stroke of the nozzle needle is set to a smaller value (PRE-LIFT) so as to reduce the injection rate, while when the engine is operating under a high speed/high load condition, the lifting stroke of the nozzle needle is set to a larger value (FULL LIFT) so as to increase the injection rate.
In these proposed fuel injection valves equipped with the above injection rate control means are employed throttle nozzles adapted to effect throttling injection and non-throttling or main injection dependent upon the lifting stroke of the nozzle needle. More specifically, when the engine is operating under a low speed/low load condition or during PRE-LIFT of the nozzle needle, the throttling injection is effected to cause ordinary combustion (by evaporation of atomized fuel), while when the engine is operating under a high speed/high load condition or during FULL LIFT of the nozzle needle, the main injection is effected to cause "M Combustion" (by evaporation of fuel adhering to the wall surface of the combustion chamber). However, according to such throttle nozzles, fuel is injected in a single direction irrespective of the mode of injection i.e. throttling injection and main injection, providing the disadvantage that part of injected atomized fuel collides with the wall surface of the combustion chamber even during throttling injection, causing increased emission of HC from the engine.